One known example of this type of lighting device is a so-called “LED in glass” device. An example is shown in FIG. 1. Typically a glass plate is used, with a transparent conductive coating (for example ITO) forming electrodes. The conductive coating is patterned in order to make the electrodes that are connected to a semiconductor LED device. The assembly is completed by laminating the glass, with the LEDs inside a thermoplastic layer (for example polyvinyl butyral, PVB).
Applications of this type of device are shelves, showcases, facades, office partitions, wall cladding, and decorative lighting. The lighting device can be used for illumination of other objects, for display of an image, or simply for decorative purposes.
One problem with this type of device is that semiconductor LEDs are point sources. As a result, the LEDs appear as bright dots of light, which is not always preferred, and does not give uniform illumination.
The device is transparent when it is not illuminated, and this is a desired feature. It has been proposed to provide a scattering function within the structure, so that the point source illumination is made diffuse. However, this affects the transparency of the structure in the non-illuminating state, which is undesirable.